Add reference to #91 (to be squashed with previous commits)

matching-core/src/main/java/com/graphhopper/matching/MapMatching.java

@@ -195,7 +195,7 @@ public MatchResult doWork(List<GPXEntry> gpxList) {
         queryGraph.lookup(allQueryResults);
 
         // Different QueryResults can have the same tower node as their closest node.
-        // Hence, we now dedupe the query results of each GPX entry by their closest node.
+        // Hence, we now dedupe the query results of each GPX entry by their closest node (#91).
         // This must be done after calling queryGraph.lookup() since this replaces some of the
         // QueryResult nodes with virtual nodes. Virtual nodes are not deduped since there is at
         // most one QueryResult per edge and virtual nodes are inserted into the middle of an edge.